I agree with Duane, I think you have a slight warp in the wing or you may be creating a warp when attaching your struts. Use a level on the bottom of one wing tip, at the last rib, and shim up your floats to get the wing level, then go to the other side and check. Another way is to hold a yard stick under the wing tip and measure from the ends of the stick to the floor (table). Shim the floats till both measurements are the same. Now go to the other wing tip and check the measurements.
Seaplane